The judges rejected the defendant's claims that his interest in young girls was artistic and not sexual.

Lord Thomas said the girls had "no understanding of the true purpose" behind what Ovenden was doing.

"There was no doubt that his purpose was sexual," he said. "There is no doubt that he had a sexual interest in children."

He added Ovenden's reputation as a landscape artist enabled those who were closest to the children to trust him.

The judges heard a bid by the defendant, who denied abusing his subjects, to challenge his conviction.

He had previously admitted taking the pictures of children, including those in various states of undress, but claimed they were not indecent.

The court rejected his application for permission to appeal, ruling the verdicts were "safe".

'Punished appropriately'

Lord Thomas said the court had seen victim impact statements in which they described how giving evidence at Ovenden's trial was the worst experience of their lives.

When suspending the prison term, the sentencing judge Judge Graham Cottle said he took into account Ovenden's age, the length of time since the offences, and his "steep fall from grace and irretrievably tarnished reputation".

But it was argued on behalf of the Attorney General that "reputational impact" was not a reason for suspending the sentence.

Lord Thomas said Ovenden had shown "no contrition", maintaining that he had done nothing wrong.

Following his trial, Ovenden had claimed he was the victim of a "global witch-hunt against artists".

"It is self-evident he has no understanding of the very serious harm he has done to the victims by his serious criminal misconduct.

"He still asserts that art is being put on trial. That is nonsensical bearing in mind the facts."

Tate removed prints

Speaking after the hearing, Mr Grieve said: "Graham Ovenden committed terrible sexual offences against vulnerable young girls who were in his charge and ought to have felt safe. He manipulated them and abused his position of trust.

"The Court of Appeal agrees that the 12-month suspended sentence handed to him was unduly lenient, and I am satisfied they have replaced it with 27 months' custody.

"It is right that sexual crimes, whether committed many years ago or more recently, should be punished appropriately."

Following Ovenden's conviction, the Tate removed more than 30 prints from its online collection.